Rule 25 of 25 · Chapter IV — Numbers, Lies, and Greens
Practise with an alignment stick down and one clear feedback marker on the ground, and change only one thing per session.
Why this rule exists
Without an alignment stick you drift, and then you fix a face problem that was really an aim problem. Without a marker on the ground you have to guess where the club met the turf, which is the one fact iron practice depends on. And changing several things at once means that when something improves you don't know which change caused it.
In practice
Lay a stick on your target line or along your toes every time you practise irons, and put down a second reference — a tee just outside the ball, a line of chalk or spray, a strip of turf paint — so your divot tells you where your low point was. Pick one focus for the session, write it down, and hit every ball on that focus. Check the divot's start point and direction after each shot instead of watching the ball flight.
When it doesn't apply
Before a round, warm up without feedback aids and without changes — just find your rhythm. And once a habit is genuinely built, spend some sessions hitting varied targets and clubs with no aids at all, since the course gives you no sticks and no lines.